This invention relates to a cooking utensil for keeping warm and cooking contents therein which enable the sufficient cooking of the contents only using the remaining heat of the cooking utensil and the contents by suspending the heating thereof after boiling or after elapsing a predetermined time of boiling without releasing the nutritive values and perfumes of the food.
Generally, in boiling food in a cooking pan, the pan continues to be heated over the fire even after the contents of the pan become boiled so as to ensure that the food in the pan is sufficiently soft.
It has been found, however, that most foods do not need to be cooked at a temperature of 100.degree. C. For example, potatoes and taros can be adequately boiled at temperatures of 80.degree. C. to 90.degree. C., and when meat is boiled or cooked at temperatures of not less than 80 .degree. C., the protein thereof is completely denatured. Thus, it has become clear that it is not necessary to continue to heat most of foods in the pan after the food reaches 100.degree. C. and begins to be boiled. Basically, in cooking foods, it is only necessary for most foods to be maintained at suitable temperatures, for example of 80.degree. to 90.degree. C. for a predetermined time period, for example, of 0.3 to 1 hour. Thus, generally, although energy need to be produced to initially heat the food in the pan up to a predetermined temperature, it is not necessary to continue to heat the foods and keep the food boiling except for the purpose of evaporating water, boiling down of the contents, or the like.
In addition, as a result of various investigations, it has been almost confirmed that seasoning, in other words, the permeation of impregnation of the initially added flavorings into the foods is caused by the difference of the osmotic pressure of the water in the foods or between the soup and foods for reasons of the temperature gradients in the foods occurred at the time of temperature reduction after heating or raising the temperature thereof. Thus, it is important to reduce the temperature not abruptly but smoothly and slowly so as to season the boiled food effectively. In the case of quick reduction of the temperature, the gradient of the osmotic pressure of water in the foods becomes great and the inner pressure of the foods becomes lower than that of the outside thereof. For this reason, the structure of the foods is broken and the contraction of the foods occurs.
Furthermore, it is important not to overheat the foods so as to leave the nutrition values of the respective foods and the "flavor" which is the main elements of tastes of the respective foods after cooking. This applies to the prevention of boil crumbling.
From these findings, it became apparent that, if the temperature reducing process of the foods is rendered slow by extremely preventing the scattering or radiation of the remained heat after performing necessary heating for denaturization of the respective foods, total amounts of heat and adding amounts of water used for cooking are greatly reduced and the foods sufficiently seasoned are obtained without losing their nutrition values, their flavorings, and their original shapes.
The present inventors have proposed a pan for keeping warm and cooking which enables to effectively keep warm and cook the foods, different in its conception from the conventional cooking method as is described above(Japanese Utility Model Application No. 35484/1986) prior to the present invention.
The pan for keeping warm and cooking of the previously proposed invention has a structure as shown in FIG. 1. In the drawing, the reference numeral 1 designates the pan and the reference numeral 2 designates its lid. The pan 1 comprises an inner vessel portion 3 being cylindrical and having a bottom wall, and an outer shell portion 5 provided coaxially around the inner vessel portion 3 intervening an annual space portion 4 at a predetermined distance therewith.
The side wall of the inner vessel portion 3 is decreasing in a diameter progressively toward the bottom wall 3a, that is to say, tapering downwardly, and the upper end of the inner vessel portion 3 is directed radially to form a peripheral retainer flange 3b.
The outer shell portion 5 is formed to be of a substantially cylindrical shape, and the lower end 5a of the outer shell portion 5 is slightly bent inwardly, and the upper portion 5b thereof is largely bent inwardly. The inside diameter of the upper end 5b of the outer shell portion 5 is defined smaller than the outside diameter of the peripheral retainer flange 3b of the inner vessel portion 3.
Thus, if the inner vessel portion 3 is inserted from the upper side into the outer shell portion 5, the peripheral retainer flange 3b comes in touch and affixed to or engaged with the upper end 5b of the outer shell portion 5. Thus the inner vessel portion 3 and outer shell portion 5 are engaged to form the consolidated pan 1. Then, the pan 1 can be carried by taking a pair of hand grips 6 secured to the periphery of the outer shell portion 5.
In addition, the hand grips 6 and 6 are fixed to the opposed side surface adjacent to the upper end portion of the inner vessel portion 3. These hand grips 6 and 6 serve e.g. for taking up the pan from fire flame or transferring the pan from one place to another place similarly with the commercially provided pans.
Further, at the upper portion of the outer shell portion 5, a plurality of apertures 5b are bored with a constant interval in the horizontal direction so that the space portion 4 communicates with the atmosphere therethrough.
In the meanwhile, the lid 2 comprises an outer lid 2a and an inner lid 2b, and the outer lid 2a and the inner lid 2b are assembled integratedly in the manner that they include the space portion 2c. The inner lid 2b is made of materials having low heat conductivity and high heat resistance such as heat resistant plastics, glass or the like so as to reduce the scattering or radiation of the heat energy from the inner vessel portion 3 to the outside thereof.
Incidentally, since the lid 2 is not directly in contact with the foods to be heated in the inner vessel portion 3 and intervened by air and thus the scattering or radiation of the heat energy is little in comparison with that of the bottom portion 3a or side surface portion of the inner vessel portion 3, the effect of keeping warm can be considerably realized even if the lid 2 is constituted in a single layer instead of double layers for the purpose of costs down. At this time, if the materials with high insulating properties such as heat resistant plastics, heat resistant glass are used, the effect of keeping warm is more improved.
And then, when the cooking pan with the above construction is, for example, placed on a kitchen gas heater for heating, the fire flame does not escape outwardly intercepted by the lower portion of the outer shell portion 5. Contrary, heated air is directed toward the space portion 4 even if the fire flame of the kitchen gas heater is more or less powerful. Here, the flame and the air with high temperature do not escape outwardly except for passing through the apertures 5b since they flow through the space portion 4 as if they are aspirated in accordance with the shape of the space portion 4 which displays the "chimney effect" by means of the apertures 5a. And further, the air with high temperature entered or flowed in the space portion 4 is uniformly dispersed on the whole outer periphery of the inner vessel portion 3 in accordance with the shape of the space portion 4 formed substantially in a cylindrical configuration and with the result that the heat energy is effectively transmitted to the foods in the inner vessel portion 3.
And then, if the pan 3 is disposed or placed on a plate P as shown in FIG. 1 after boiling the contents in the pan 3 and suspending the heating, the lower end opening flange 5a of the outer shell portion 5 is tightly closed by the plate P and this causes the loss for the passage of the air with high temperature and the heat energy stored in the space portion 4 is preserved without escaping outwardly in spite of the presence of the apertures 5b. The heat in the pan 4 is not scattered outwardly because the heat energy being stored, and the inside of the pan is kept at high temperature for a long time if the pan is closed by the lid 2. As the result, in the case of using this pan, the permeation or impregnation of the taste into the foods can be sufficiently done since the cooking is achieved sufficiently only using the energy necessary up to the initial boiling and the amount of added water is reduced and the reduction of the temperature is achieved very slowly.
Furthermore, the scattering or radiation of the heat energy is more reduced since the inner vessel portion 3 and the outer shell portion 5 are slightly in contact with each other and the contact area thereof is very small upon using the pan, which causes the less transmission of the heat from the inner vessel portion 3 to the outer shell portion 5. In addition, the cleaning of the pan 1 can be readily performed since the pan 1 can be readily disassembled after the completion of using it. Furthermore, a multiplicity of the inner vessel portions and the outer shell portions can be put one over the other, respectively, and is possible to receive them in a small space since the pan can be disassembled to its inner vessel portion 3 and the outer shell portion 5 and the inner vessel portion 3 is decreased in a diameter toward the bottom portion thereof and the outer shell portion 5 is rendered to be slightly decreased in a diameter because of its cylindrical configuration.
The advantages of the pan for keeping warm and cooking and the cooking method using the same which are put to initial practical uses are summarized as follows;
(1) energy-saving;
The pan saves the energy since the efficiency of the heating is superior and it is not necessary to be cooking over a slow fire.
(2) reduction of labor;
The method for keeping warm and cooking using the pan reduces the labor for cooking since the heating period is for a few minutes until the boiling of the contents in the inner vessel portion 3 occurs and the cooking is completed only by leaving the boiled foods while cooking over a slow fire for a long time using commercially provided pan needs labors. In addition, in the case of using the pan for keeping warm and cooking, burning of the foods with carelessness is prevented.
(3) The cooked foods are kept warm for a long time.
(4) The flavor of the cooked foods is not dispersed, that is, the cooked foods are delicious.
(5) The heat up by the fire is uniform.
(6) Gas ranges can be used effectively because the pan occupies the ranges only shortly.
(7) The cooked foods are delicious and the decomposition of the nutrition thereof is little because they are not boiled too excess.
However, as a result of further investigations so as to put the pan for keeping warm and cooking described hereinbefore in practical and economical use, the inventors have found the points to be improved as follows.
That is, at the present time, there exist gas ranges of various sizes as heat sources in a general family, and not restricted to them, further exist ranges which heat using a flat heating plates such as an electric range, an elecromagnetic cooking device or the like. Thus, it is necessary to render the pan described hereinbefore fitting to the ranges of various sizes or the heat sources such as electric ranges, electromagnetic cooking devices or the like.
In the meanwhile, in the conventional pan for keeping warm and cooking, the lower end portion 5a of the outer shell portion 5 projects lower than the bottom portion 3a of the inner vessel portion 3 as shown in FIG. 1. Such a structure is necessary to prevent the scattering or radiation of the heat by rendering the bottom portion 3a of the inner vessel portion 3 not tightly in contact with the flat plane and facing the bottom portion 3a to the plane intervening with an air layer when the pan is disposed or placed on the plane by putting out the fire after completion of heating.
However, in the case of using the pan for keeping warm and cooking at home, it occurs sometimes that the trivet of the gas range is not extended to the periphery thereof in substantially the same diameter as that of the outer shell portion 5 depending on the size of the kitchen gas range used. Thus, in such a case, it is difficult to dispose or place the pan steadily on the trivet and further such an operation is very dangerous since the pan may get out from a part of the trivet to incline on the trivet, and optionally there is a fear to spill the contents of the pan.
In addition, in the case where the heat source used is an electric range or an electromagnetic cooking device, it is desirable that the bottom portion 3a of the inner vessel portion 3 is tightly in contact with the heating surface of the heater. However, taking into consideration of such a convenience and if the lower end 5a of the outer shell portion 5 is aligned to the same horizontal plane as that of the bottom portion 3a of the inner vessel portion 3, the bottom portion 3a of the inner vessel portion 3 tightly contacts with the supporting surface and the air layer required to keep warm is not formed. Consequently, the effect of keeping warm is significantly reduced upon putting out the pan from the fire and keeping warm the contents in the inner vessel portion 3. Of course, the effect of keeping warm of the pan may be increased if the plate of insulating materials such as expandable polystyrene is used as a exclusive sheet for placing the pan. However, the constitution of the pan for keeping warm and cooking in which the air layer is formed under the bottom portion 3a of the inner vessel portion 3 upon placing on the plane would be more convenient because it is not necessary to particularly restrict the positioning place. Such a convenience is very important in the kitchen where the pans are always used.
In addition, the upper portion of the space portion 4 between the inner vessel portion 3 and the outer shell portion 5 of the conventional pan is closed and is constituted so as to render the burnt gas in the space portion 4 exiting to the atmosphere from the apertures 5b provided on the upper portion of the outer shell portion 5. However, when the area of the exit for the heated air is relatively small as the apertures 5b, the flow rate of the warmed air of the burnt gas rising in the space portion 4 is slow and the amount of the air derived from the outside thereof through the bottom portion 3a of the pan 1 is little. For this reason, the temperature of the burnt gas in the space portion 4 is not lowered and the outer shell portion 5 is heated too excess by the vapor with high temperature to a high temperature(about 450.degree. C.).
Further, in the conventional pan for keeping warm and cooking described hereinbefore, a peripheral retainer flange(upper end portion 5c) for engaging with the inner vessel portion 3 is required to be mounted near the upper end portion of the outer shell portion 5 and this causes the high costs for producing the outer shell portion 5.